Suggestion for Mechanism of Strengthening of “Nanotoughened” Ceramics

This work seeks to explain the mechanism of the dramatic strength increase obtained by dispersing nanometer sized particles within a monolithic ceramic matrix relative to the pure matrix material. The crack tip toughness, along with long crack toughness of the material, is experimentally investigated, along with slow crack growth rates. A simple consideration of Griffith criteria shows that strength increases cannot be explained simply in terms of increased toughness. Additionally, critical crack sizes for fracture are considerably smaller than the grain size. It is proposed therefore that the inclusion of the nanoparticles changes the residual stress conditions within the material, hindering microcrack initiation in the stress field around a pore and reducing the facet length of such microcracks.